Does materialize.io have a trigger system yet though? One of the great things about Rethink was that client libraries made it easy to have application code stream live changes over websocket etc. to a client.
Yes, we do! It's a little non-standard SQL syntax we added called TAIL. You write TAIL <viewname>, and you get changes pushed to you. You can see a video of me badly explaining it in [2]. You can also do the thing where you create a Kafka SINK of a view and have the system push this to Kafka rather than have a long-running open SQL connection. There's some fun stuff with TAIL AS OF (start the changes at a specific point in time) and TAIL WITH SNAPSHOT (run a SELECT query, and then begin the change stream transactionally with the time of that SELECT query) that you can read about in the docs[1].